State of the art PLT (Power Line Telecommunications) may cause coexistence limitations with broadcasting services. The publication ETSI TS 105 578; PowerLine Telecommunications; “Coexistence between PLT modems and short wave radio broadcasting services”; ETSI 2008 describes an adaptive frequency notching technique, which on the one hand has minimum impact on data throughput and QoS (Quality of Service) requirements and, on the other hand reduces interference between PLT (Power Line Telecommunications) and short wave radio broadcast.
Communications and powerline wires act as bidirectional antennas, wherein typically the transfer function or antenna gain is identical for signal radiation and for signal reception. Communications and powerline wires that are suitable for receiving a broadcast signal and that transmit signals in the same frequency band can disturb the reception of the broadcast signal at a radio receiver. Adaptive notching suppresses the use of frequency bands in which broadcast signals are detected by the communications system.
PLT modems detect the presence of broadcast signals by sensing a “noise”. The use of the term noise in this application follows the terminology fixed in the ETSI TS 105 578 publication, wherein noise includes radio broadcast signals picked up on the mains cabling. As described in EP 2 020 758 A 1, broadcast signals on power lines may be detected, by way of example, by measuring a received signal power in a plurality of narrow frequency bands.
Having identified frequency bands used by receivable radio broadcast signals, the PLT transmitter omits the identified frequency bands by inserting a notch into the transmission spectrum. The notch may be applied by providing suitable notching filters, for example a digital filter with suitable filter coefficients.
WO 2008/101593 A1 describes a transmitting method which is based on a multiple carrier modulation technique and adaptive frequency notching, wherein such carriers are amplified, which are adjacent to the notched frequency bands and which are attenuated by the notching filter.
It is an object of the invention to provide a method and devices for detecting of broadcast signal ingress in communications systems reliably and timely.
The object is achieved by a communications systems according to claim 1, by communications devices adapted for the communications systems as they are claimed in claims 8 and 10 and by a method for operating a communications system as claimed in claim 11. Further embodiments are defined in the dependent claims respectively. Details of the invention will become more apparent from the following description of embodiments in connection with the accompanying drawings.